He told IT experts from major companies, who were invited to a Home Office event in Westminster to begin work on the database project: “The police, the Child Exploitation and Online Protection centre (CEOP) are doing excellent work in difficult circumstances.

“But that key threat to our children is ever growing and changing so it is critical for the National Crime Agency and wider UK law enforcement to be equipped to tackle this sickening crime.”

Mr Green said that a Home Office survey carried out in 1990 estimated that just 7,000 images of child sexual abuse were in circulation - as hard copies - in this country.

“Today the growth and development of the internet means that the number of these images online is in the millions,” he said.

“And the number of individual children depicted in these images, and therefore desperately in need of our protection, is likely to be in the tens of thousands.”

He went on: “It isn’t sufficient to simply prosecute those offenders who possess such images. We have a duty, and moral obligation, to find those children who are being abused, and protect them, whether they are in the UK or abroad.

“Police forces have recorded cases where individual offenders have possessed up to 2.5 million images.”

It will need “new thinking” to tackle the issue, said the minister.

The database, which Mr Green said he hoped would be oeprational by the end of the year, will link up existing “fragmented” police databases to create a “single secure database of illegal images of children”.

It would help speed up investigations by reducing the amount of work duplicated by different agencies and help identify victims more quickly, he added.